The invention relates generally to monitoring and control systems and more particularly to a method and system for monitoring a temperature of batteries.
A wide variety of applications employ batteries and battery banks for operation. These range from mobile applications to consumer uses to industrial applications, to mention just a few. Vehicle and other mobile applications, for example, commonly use one or more batteries either for starting and auxiliary functions, or for a primary or secondary source of power for normal operation. In recent years, for example, electrical vehicles and hybrid electrical/engine driven vehicles have become the focus of intense development activities. Such vehicles represent a demanding environment in which battery performance and life are important to the continued reliable operation of the vehicular systems.
Battery systems used in many applications, such as electrical and hybrid vehicles, may contain many battery modules, each further containing one or more individual batteries. These batteries individually may have low voltages, of about 1.2 volts. However, in applications such as in hybrid vehicles, where the battery systems contain a large number of individual batteries, the voltage gradient is very high. Moreover, in hybrid vehicles, high-energy density batteries are used, which typically charge and discharge rapidly. These new modes of operation subject the batteries to higher electrical loads. Consequently, thermal management of battery systems becomes a critical issue. In addition, for cooling the battery systems, an effective temperature measurement scheme is needed. Therefore, it is desirable to have a temperature profile, for proper control and corrective actions to be taken.
Current battery temperature measurement schemes generally include ways to measure temperature outside the vehicle battery and within it. As is well known, measurement techniques involve measuring the vehicle battery temperature using thermocouple sensors and “temperature dependent resistor” or “resistance temperature device”, also referred to as an “RTD”.
One disadvantage of RTDs is that, a suitable electrical power supply is required for its operation. A small change in the current or voltage of the power supply may cause an erroneous measurement of the temperature. Similarly, thermocouples also operate using power supplies and are also susceptible to any kind of electrical interference.
One method to overcome the problem of electrical interference is to use fewer RTDs or thermocouple sensors to measure the temperature of batteries. However, such a scheme would provide only a limited temperature profile of the battery system.
Other measurement schemes involve measuring temperatures of the battery system indirectly by measuring the temperature of the vehicle motor and the environmental temperature. However, these do not give the true temperature of the battery system. Temperature sensing integrated circuit chips have also been employed to measure the temperature. These chips exhibit a proportional increase in voltage signal outputted with the increase in temperature. Again, these have the limitation of being able to measure only the external temperature.
It would therefore be desirable to obtain true temperature measurement of the battery system. Also desirable would be a detailed temperature profile in order to efficiently monitor and control the battery systems.